Method and apparatus for cupola emission control

ABSTRACT

A cupola emission control system is disclosed which includes a cylindrical cap assembly adapted to be mounted on top of a cupola flue so that gases from the cupola enter the assembly through an opening in the bottom thereof. The top of the cap assembly is defined by a pair of doors adapted to be opened to open the cap to atmosphere. Opposed side wall portions of the cap are provided with openings, one of which is an ambient air opening and the other of which is a mixture outlet opening. Fan means is disposed in a ductway leading to the air inlet opening so that ambient air under positive pressure can be introduced into the cap for dilution and cooling in the cap of gases from the furnace. The outlet opening is connected to a pair of separator units which are serially arranged between the cap housing and an exhaust stack for the system. An exhaust fan is associated with the output side of the second separator leading to the stack in order to induce flow of furnace gases through the system to the stack.

Barnes, Jr.

[451 July 10, 1973' METHOD AND APPARATUS FOR CUPOLA EMISSION CONTROL[75] Inventor: Thomas Donald Barnes, Jr.,

Burlington, Ontario, Canada [73] Assignee: Don Barnes Ltd., Hamilton,Ontario,

Canada [22] Filed: Feb. 25, 1971 21 Appl. No.: 118,926

[52] US. Cl 55/83, 55/257, 26l/D1G. 9 [51] Int. Cl....'. B0111 50/00[58] Field of Search 55/83, 84, 89, 72, 55/9, 257, DIG. 30; 261/016. 9,17; 266/16, 17

[56] References Cited UNITED STATES PATENTS 2,729,301 l/l956 Ekstrom,Jr. ..'55/257 2,940,733 6/1960 Umbricht... 55/257 3,382,649 5/1968Richmond..... 55/84 3,477,203 11/1969 Luge et 55/9 2,618,548 11/1952Drake 266/17 3,315,444 4/1967 Seversky... 55/257 3,406,012 10/1968 Rahn55/72 Primary Examiner-Charles N. Hart Attorney-Meyer, Tilberry and Body[57 ABSTRACT A cupola emission control system is disclosed whichincludes a cylindrical cap assembly adapted to be mounted on top of acupola flue so that gases from the cupola enter the assembly through anopening in the bottom thereof. The top of the cap assembly is defined bya pair of doors adapted to be opened to open the cap to atmosphere.Opposed side wall portions of the cap are provided with openings, one ofwhich is an ambient air opening and the other of which is a mixtureoutlet opening. Fan means is disposed in a ductway leading to the airinlet opening so that ambient air under positive pressure can beintroduced into the cap for dilution and cooling in the cap of gasesfrom the furnace. The outlet opening is connected to a pair of separatorunits which are serially arranged between the cap housing and an exhauststack forthe system. An exhaust fan is associated with the output sideof the second separator leading to the stack in order to induce flow offurnace gases through the system to the stack.

22 Claims, 2 Drawing Figures INVENTOR. THOMAS D. BARNES JR.

ATTORNEYS METHOD AND APPARATUS FOR CUPOLA EMISSION CONTROL The presentinvention relates to furnace emission control systems and, moreparticularly, to a method and apparatus for cupola emission control.

In furnace systems heretofore known, such as cupola furnace systems,draft effecting arrangements have been employed to control the varyingmelting processes within the furace and to exhaust furnace gases throughparticle separating and collecting apparatus to clean the exhaust gasesprior to emission thereof into the atmosphere. Such prior art systemsmay include acap structure disposed atop the furnace flue, and a suc-'tion fan or the like disposed down stream from the cap structure andoperated to maintain a desired flow of air through the furnace chargedoor and into the flue and cap and thence into the separator apparatusand exhaust stack. In certain instances, the prior art system includethe provision of a damper controlled opening in the cap to permit theexhaust of furnace gases directly to atmosphere or to permit inducedflow of air into the cap structure by the exhaust fan for cooling theexhaust gases as they travel along the path to the separator apparatusand the exhaust stack.

Cupola emission control systems of the above character fail to providesatisfactory furnace process control commensurate with desirable furnacegas emission control. Moreover, the induced cooling air arrangementsnecessitate the use of expensive high-alloy stainless orrefractory-lined take-off ducting from the cap assembly because of theinability of these systems to otherwise accommodate the extremely highemission gas temperatures realized during certain periods of furnaceoperation. In this respect, the gas temperatures coming from the surfaceof a charge in the furnace under normal cupola operating conditions isin the range of 450 to 700 F. During a bum-down condition, however, suchas at the end of the operating cycle when the charges are allowed tomelt down in thecupola resulting in low burden levels, the heat of gasesin the cupola flue at the cap will be as high as l,700 to 2,000F andlive flames from the furnace may rise in the stack all the way to thecap. With an induced cooling air arrangement of the character heretoforeknown, air introduced at the cap point through a damper or doorcontrolled opening results in laminar flow of air and furnace gasstreams in the take-off pipe or conduit leading from the cap. Suchlaminar flow continues for a considerable distance in the take offconduit before natural mixing of the air and gases occurs due to thekinetics of gas streams. Thus, the more costly materials mentioned aboveare required in fabricating the cap and the cap take-off pipe or exhaustducting in order to handle the high temperatures in these components ofthe system resulting from the slow mixing of air and hot furnace gases.Moreover, the cap structure itself is disadvantageously subjected to thehigh temperature conditions of the flue gases and furnace flames. Itwill be appreciated too that in the systems heretofore known, the slowcooling of furnace gases resulting from laminar flow of air and gasstreams results in a relatively high temperature of the'gases when theyreach the exhaust fan. Thus, the fan as well as the separator equipmentthrough which the gases pass in traveling toward the fan aredisadvantageously subjected to undesirably high temperatures whichadversely affect the life thereof. r

In addition to the inability of earlier systems to provide for anadequate amount of cooling of furnace gases and system components,little or no control can be exercised with regard to the total volume ofgases and air flowing through the system at a given time or .underfurnace operating conditions. Such control is highly desirable andadvantageous in that for a range of operating temperatures for a givenfurnace, more efficient and effective emission temperature control canbe achieved when the total gas and air volume in the system can beaccurately maintained regardless of changing operating conditions withinthe furnace. In the past, cooling air has been introduced with little orno control of thevolume thereof.

The emission control system of the present invention advantageouslyovercomes the drawbacks of the prior art arrangements including thosespecifically mentioned above and, in this respect, provides a constantvolume emission control system which is capable of handling a wide rangeof temperatures and initial gas volumes coming from the melting zone ofa cupola so that absolute temperature control of gases entering theexhaust stack can be achieved. In the system of the present invention,the temperature of gases emitted from the furnace is controlledimmediately at the cap in a manner whereby, regardless of the widetemperature range of these gases in the flue of from about 450 to 2,000F, the exhaust stack temperatures can be maintained below about 650 F.This is achieved by reducing the temperature of the furnace gases at thecap to a range of about 600 to 700 F even when the furnace gasesentering the cap are in the upper vicinities of the 450 to 2,000 Frange. It will be appreciated that such control of the temperatures ofthe furnace gases at the cap advantageously eliminates the necessity ofemploying the costly materials heretofore required for the cap take-offducting in order to handle the high temperatures of the gases. Moreover,the temperature control protects the exhaust fan and separator equipmentand provides for more accurate and efficient cupola operation.

The foregoing advantages are achieved in the present invention bypositively forcing ambinet air directly into the cap structure with ahigh velocity so that the hot particle laden furnace gases entering thecap area are immediately mixed with the air and are thereby subjected toconsiderable cooling and dilution by the air before leaving the cap. Asis well known in cupola fur nace operation, air is admitted to the fluethrough the charging door in a controlled volume for mixture with thefurnace gases from the melting area of the furnace as they rise in theflue. As used herein, the term furnace gases is intended to includedraft air and the gases emitted directly from the melting area of thefurnace. The ambient air forced into the cap is a pre-calculated amountof air designed to provide a constant volume for agive'n furnace size.The forced air is introduced into the cap area under high velocity inorder to achieve immediate furnace gas-air mixing in the cap. This highvelocity charge of air in addition to cooling the furnace gases,provides for diluting the particle laden furnace gases and for providingtemperature protection for the cap structure even in the most extremehigh temperature operating conditions of the cupola.

' Moreover, the forced dilution and constant volume operatingcharacteristics of the system of this invention operate to maintaincarbon monoxide in the exhaust gases at a desirably low level and toprovide for more efficient separation of the particles from the furnacegases, thus to advantageously reduce the pollution level of gasesexhausted to atmosphere.

It is to be noted too that the high velocity forced air addition at thecupola cap area, by maintaining a cap exhaust temperature level in therange of about 600 to 700 F, protects the downstream equipment includingthe exhaust fan and separator components from the adverse affectsof hightemperature and eliminates the necessity of any external cooling meansfor the upstream equipment and ductwork such as cooling water which hasbeen employed in the past. Use of cooling water disadvantageously causescorrosion of metallic components in the system, is subject to freezingproblems during cold weather and involves the use of expensive flowcontrolling devices. A further advantages of the system of the presentinvention is the fact that by maintaining constant gas-air volumes,constant efficiency in particle collection by the separating equipmentis realized independent of the melt rate of the furnace.

Accordingly, it is an outstanding object of the present invention toprovide a furnace emission control system which advantageously operatesto cool and dilute hot particle ladden furnace gases, thus to protectsystem equipment from adverse temperatures and more efficiently providefor separation of particles from the gases and reduce the level ofpollutants therein and thereby advantageously reduce the pollution leveland temperature of gases ultimately exhausted from the system.

A further object of the present invention to to provide a furnaceemission control system adapted to handle a wide range of exhausttemperatures and gas volumes coming from the operating zone of a furnacein a manner whereby absolute temperature control of the gases enteringthe exhaust stack of the system is achieved.

Another object of the invention is to provide a furnace emission controlsystem in which high velocity force air is added to the furnace gases tothe top of the furnace flue to achieve immediate gas diluting andcooling, whereby absolute temperature control of gases entering theexhaust stack can be achieved.

Another object is the provision of a furnace emission control system ofthe character mentioned wherein a constant volume of high velocityforced air is added to furnace gases to achieve cooling of furnace gasesto a desired low exhaust temperature and to maintain a constant gas-airvolume in the system.

A further object of the present invention is to provide a furnaceemission control system in which a cap assembly of the system receiveshigh velocity ambient air under positive pressure directly thereinto toprovide temperature protection for the cap assembly even under the mostextreme high temperature operating conditions of the furnace.

Yet another object of the present invention is to provide a furnaceemission control system in which the necessity for the use of hightemperature resistance materials heretofore required is advantageouslyeliminated.

Still another object of the present invention is the provision of amethod of cooling cupola furnace emission gases in a manner to achievegreater temperature reduction of the gases leaving the cupola flue thanheretofore possible.

Still a further object is to provide a method of treating cupolaemission gases to facilitate cooling and particle removal therefrom withgreater efficiency than heretofore known.

Still another object is the provision of a furnace emission controlsystem including a cap structure adapted to be mounted on top of anexisting furnace flue and defining a chamber into which furnace gasescan flow and in which the gases are cooled and diluted by introductionof a high velocity stream of air under positive pressure directly intothe cap, and which cap is provided with movable opening means to permitdirect exhaustion of furnace gases to atmosphere.

Other objects will in part be obvious and in part more fully pointed outhereinafter in conjunction with the description of the drawing whichillustrates a preferred embodiment of the invention and in which:

FIG. 1 is aside elevation view of the emission control system of thepresent invention in its entirety; and

FIG. 2 is a plan view section of the cap structure of the system takenalong the line 2-2 in FIG.- 1.

Referring now in particular to the drawing, there is illustrated in FIG.l a cupola 10 including a refractory lined, steel jacket flue 11, acharging door or opening 12 and a pressure air trunk 13. Trunk 13 issupplied with air from a pipe 14 which in turn receives air underpressure in a well known manner from any suitable source. As is wellknown to those skilled in the art of cupola furnaces, materials to betreated therein are introduced through the charging door, and combustionis maintained by an air blast through tuyers extending inwardly from theair trunk 13 at the bottom of the cupola. During operation of the cupolaa controlled draft enters the charging door for flow upwardly thereinwith gases from the furnace. Simultaneous control of the combustion airand the suction draft facilitates effective regulation of the combustionprocess within the eupola. In accordance with known practice, a gasfired after-burner 15 may be provided in the flue of the cupola toeliminate carbon monoxide gas and to reduce odor emission from thecupola.

In accordance with the present invention, furnace emission controlapparatus is provided which includes cap means 16 including acylindrical housing 17 adapted to be suitably mounted on the furnaceflue 11. Housing configurations other than cylindrical could, of course,be employed. The emission control apparatus further includes separatormeans 18 disposed between exhaust conduit means 119 leading from the caphousing and an exhaust stack 20. Conduit means 159 may be anon-corroding steel. Separator means 18 preferably is defined byserially arranged separator units 21 and 22, separator 21 being a heavyparticle collector and separator 22 preferably being a cyclone typecollector. The specific separator structure is not pertinent to the present invention, and any suitable separator or precipitator apparatus maybe employed. A motor operated exhaust fan 23 is disposed on the outputside of separator 22, and the output of the exhaust fan leads to exhauststack 20 through exhaust duct 24.

The cylindrical cap housing 17 includes, as illustrated in FIGS. 1 and2, a bottom opening 25, cylindrical sidewall means 26 and movableclosure means 27 overlying sidewall means 26 and defining a cap chamber28 therewith. Cap sidewall means 26 is defined by a steel shell 26a andrefractory lining 26b and thus, in effect defines an extension of fluell. Thus, the cap section could be integral with stack 11. Openingdefines a gas inlet leading into chamber 28 from flue 22. Opposedcylindrical openings 29 and 30 are provided in wall means 26 andrespectively define an air inlet and a mixture outlet for the caphousing. Cylindrical'air inlet conduit means 31, preferably of steelconstruction, extends laterally'outwardly from sidewall means 26 insurrounding relationship with regard to opening 29 in the sidewallmeans. Conduit means 31 includes a conical wall portion 32 disposedbetween the entrance end 33 of the conduit means and sidewall means 26.Air pump means, here in the form of a motor driven fan 34, is disposedin conduit means 31, and baffle means is disposed in the conduit meansbetween fan 34 and opening 29 in sidewall means 26. Preferably bafflemeans 35 is in the form of a cone-shaped component disposed in conduitmeans 31 with the smaller diameter end thereof facing toward the fan.Conical wall portion 32 of conduit means 31 conforms substantially tothe contour of cone-shaped baffle 35. The cone may, if desired, bemounted to be axially reciprocated relative to conduit means 31 thus toincrease and decrease the space 36 between baffle 35 and conical wallportion 32 to facilitate varying the velocity of inlet forced air.

Opening 30 in sidewall means 26 defining the mixture outlet issurrounded by cylindrical, tapered ductwork section 37, extendinglaterally from sidewall means 26 and suitably connected at its outer end38 to conduit 19. Ductwork section 37 preferably is unlined stainlesssteel. The axes of air inlet opening 29 and mixture outlet opening 30are substantially parallel and, although the openings are preferably inopposed portions of sidewall means 26 of the cap housing, it is to beclearly understood that the openings could be otherwise orientedrelation to the housing. It will be further noted in the preferredembodiment that the axes of air inlet opening 29 and mixture outletopening 30 are disposed substantially perpendicular to the axis of gasinlet opening 25. It will be appreciated, however, that other angularrelationships can be employed, still within the present invention.

Movable closure means 27 is defined in the preferred embodiment by apair of steel door elements 39 and 40 hingedly associated with caphousing 17 by means of suitable corresponding hinge assemblies 41 and42. Portions 39a and 40a of door elements 39 and 40, respectively,extend laterally beyond the corresponding hinge assemblies to definecounterweight means adapted to bias the door elements toward an opendisposition as depicted by broken lines in FIG. 1. The latterarrangement is defined by pulleys 43 rotatably supported by sidewallmeans 26 of housing 17 and cables 44 suitably attached to the respectivedoors and trained about the corresponding pulleys to a common linkelement 45. Link 45 is in turn connected to one end of cable 46 havingits opposite end suitably interconnected with the piston rod of an aircylinder 47. Air cylinder 47 is charged to pull downwardly on cable 46,thus to maintain doors 39 and 40 in a closed disposition. The aircylinder may be manually actuated to release the doors for movementthereof to the open position under the influence of the counterweightportions 39a and 40a thereof. Further, cylinder 47 may be adversecondition controlled in order to provide for automatic release of thedoors in response to an adverse condition which dictates that thefurnace gases should be exhausted directly to atmosphere. For example,the

cylinder may be controlled by a thermostat 48 in duct 24 to open the capdoors in response to undesirably high temperature of exhaust gases.

Fan 34 is adapted to draw ambient air into conduit means 31 and to forcethis air under positive pressure directly into chamber 28 of the caphousing. This ambient air mixes and comingles with the hot, particleladen flue gases immediately in the chamber of the cap housing to cooland dilute the furnace gases to a substantially lower temperature thanthe temperature thereof upon entering the chamber through gas inlet 25.This cooling and diluting in the chamber is made'possible by a highvelocity flow of a predetermined and controllable volume of ambient airdirectly into the chamber. Baffle means 35 provides for introducing thecooling and diluting air laterally into the chamber in a desired flowpattern. The preferred flow pattern is an annular pattern such as thatwhich is provided by the conical configuration of baffle 35. Such apattern provides for a portion of the ambient inlet air to pass adjacentthe underside of door elements 39 and 40, thus to cool the door elementsand protect these elements against the adverse effects of the hightemperature furnace gases enterring the cap housing. Further, theannular pattern of flow of ambient air provides for a portion of the airto intercept the furnace gases immediately as they enter the bottom ofchamber 28 of the housing, thus to promptly initiate the cooling anddiluting of the gases by the ambient air. The direction of inlet airflow, transverse to the direction of the gas inlet flow to the chamher,is also desirable in that it effects a condition of turbulance in thechamber by which a more rapid and thorough mixing, cooling and dilutingof the particle laden gases is achieved. It will be appreciated that fan34 can be positioned other than in axial alignment with duct means 31.For example, the fan can be vertically oriented and the flow therefromdirected into the horizontal duct 31 by suitable elbow duct means.

Although the cone-shaped baffle 35 is preferred it will be readilyunderstood that other baffle means may be employed, such as for examplean annular plate baffle or vein elements disposed in conduit means 31.it will be appreciated too that with such other types of baffle means,the baffle elements could be made to be readily adjustable to providethe desired direction of flow for the inlet air.

Fan 34 is driven by an electric motor or other source of power and isadapted to positively pump a given constant volume of air into the capchamber to achieve the desired cooling effect. The volume of forced airintroduced is precalculated dependent on furnace size, and fan 34 isdriven continuously during furnace operation to deliver the calculatedvolume of ambient air.

Exhaust fan 23 is, of course, operated continuously during furnaceoperation and is of a capacity depending on furnace size, thus to assurea proper draft through the charging door and a constant volume offurnace gas flow upwardly to the cap and thence through the separatorapparatus to the stack. It should be distinctly understood at thispoint, however, that although the volume of ambient air forced into thecap chamber is a function of the total volume of gases and air in thesystem, including the furnace gases and draft air, the amount of ambientair input is precalculated to correspond with the operating conditionsand requirements of a given cupola but does not in and of itselfmaterially effect the gas-air flow induced by the exhaust fan. Theambient air fan, in other words, is not relied upon to cause gas-airflow through the system to the exhaust stack.

As mentioned hereinabove, the specific volume of forced air addition andthe volume of gases and air drawn through the system by the exhaust fanare dependent in each instance on furnace size. Once established,however, these volumes remain constant for a given furnace throughoutfurnace operation and during varying temperature conditions of suchoperation. De-

. pending on furnace size, forced air addition generally will be in therange of 4,000 to 12,000 c.f.m. The exhaust fan will also be operated inaccordance with furnace size and generally will induce gas-air flowthrough the system in the range of 28,000 to l l5,000 c.f.m. The presentinvention provides for constant volume operation of the system, and as aresult of constant volume addition of high velocity ambient air, exhauststack temperatures are maintainable at below about 600 F even duringperiods of operation during which furnace gases entering the cap areaapproach 2,000 F. Moreover, forced addition of ambient air under highvelocity and pattern control reduces furnace gas temperaturesapproaching 2,000 F in the flue immediately in the cap area to a lowrange of 600 to 700 F which advantageously avoids the necessity of usingrefractory lined ductwork on the outlet side of the cap. Furnace systemssimply relying on induced air addition experience a gas temperature inthe cap area several hundred degrees above the 600 to 700F and thusrequire the use of expensive refractory lined ductowrk to handle thehigh temperature gases.

The apparatus of the present invention has been described hereinabove inconjunction with a preferred structural embodiment. Various changes maybe made in this embodiment, however, without departing from the intendedspirit and scope of the present invention as defined in the appendedclaims.

I claim:

1. Apparatus for use in an emission control system for a furnace havinga flue comprising, a housing at the upper end of said flue, said housinghaving a gas inlet, an air inlet and a mixture outlet, said housingbeing adapted to receive, hot particle laden gases from said furnace,flow inducing means for drawing said furnace gases into said housingthrough said gas inlet, conduit means surrounding said air inlet, andair pump means in said conduit means and spaced from said air inlet forforcing ambient air under positive pressure directly into said housingthrough said air inlet for said air to mix with, cool and dilute saidgases in said housing, said flow inducing means drawing said cooleddiluted gases through said mixture outlet.

2. Apparatus of the character set forth in claim ll, wherein the axes ofsaid air inlet and said gas inlet are substantially perpendicular to oneanother.

3. Apparatus of the character set forth in claim 2 wherein the axis ofsaid mixture outlet is substantially parallel to the axis of said airinlet.

4. Apparatus for use in an emission control system for a furnace havinga flue comprising, a housing at the upper end of said flue, said housinghaving a gas inlet, an air inlet and a mixture outlet, said housingbeing adapted to receive hot, particle laden gases from said furnace,flow inducing means for drawing said furnace gases into said housingthrough said gas inlet, and air pump means for forcing ambient air underpositive pressure directly into said housing through said air inlet forsaid air to mix with, cool and dilute said gases in said housing, saidflow inducing means drawing said cooled diluted gases through saidmixture outlet, conduit means surrounding said air pump means and airinlet, and means within said conduit means for controlling the path ofair flow into said housing.

5. Apparatus of the character set forth in claim 4, wherein said meanswithin said conduit means'is baffle means disposed between said air pumpmeans and air inlet.

6. Apparatus for use in a furnace emission control system comprising, ahousing having a gas inlet, an air inlet and a mixture outlet, saidhousing being adapted to receive hot, particle laden gases from saidfurnace, flow inducing means for drawing said furnace gases into saidhousing through said gas inlet, an air pump for forcing ambient airunder positive pressure directly into said housing through said airinlet for said air to mix with, cool and dilute said gases in saidhousing, said flow inducing means drawing said cooled diluted gasesthrough said mixture outlet, conduit means surrounding said air pump andair inlet, and baffle means within said conduit means between said airpump and air inlet, said baffle means' being cone-shaped and disposed insaid conduit means with the smaller diameter end thereof facing towardsaid air pump, said conduit means including a conical wall portionsurrounding said cone-shaped baffle means and radially spaced therefromto define an annular passageway for directing said air into said housingin an annular path.

7. Apparatus of the character set forth in claim 6, wherein saidcone-shaped baffle means is axially adjustable relative to said conduitmeans to selectively increase or decrease the radial space between thebaffle means and conical wall portion of said conduit means, thus tovary the size of said annular passageway and vary the velocity of airflow into said housing.

8. Apparatus of the character set forth in claim 1, and furtherincluding exhaust stack means, means for directing the flow of saidcooled diluted furnace gases from said mixture outlet to said exhauststack means.

9. Apparatus of the character set forth in claim 8, wherein said meansfor directing flow of said cooled diluted furnace gases includesserially arranged separator means for separating particles from saidcooled diluted gases, said separator means being disposed between saidgas outlet and said exhaust stack means, and said flow inducing meansbeing exhaust fan means between said separator means and said stackmeans. I

10. Apparatus for use in a furnace emission control system comprising acap housing mountable on top of a furnace flue and including side wallmeans and movable closure means, the bottom of said housing being opento said flue to define a gas inlet to said housing, said side wall meanshaving opposed air inlet and mixture outlet openings therein, saidhousing being adapted to receive hot, particle laden gases from saidfurnace flue through said gas inlet, flow inducing means for drawingsaid furnace gases into said housing through said gas inlet, conduitmeans surrounding said air inlet, and air pump means in said conduitmeans and spaced from said air inlet for forcing ambient air underpositive pressure directly into said housing through said air inlet forsaid air to mix with, cool and dilute said gases in said housing, saidflow inducing means drawing said cooled diluted gases through saidmixture outlet,

to said flue to define a gas inlet to said housing, said sidewall meanshaving opposed air inlet and mixture outlet openings therein, saidhousing being adapted to receive hot, particle laden gases from saidfurnace flue through said gas inlet, flow inducing means for drawingsaid furnace gases into said housing through said gas inlet, an air pumpfor forcing ambient air under positive pressure directly into saidhousing through said air inlet for said air to mix with, cool and dilutesaid gases in said housing, said flow inducing means drawing said cooleddiluted gases through said mixture outlet, said 15. Apparatus of thecharacter set forth in claim 10, wherein said closure means is a pair ofdoors biased toward an open disposition relative to said housing, andmeans releasably retaining said doors in a closed disposition againstsaid bias.

16. Apparatus of the character set forth in claim 15, wherein saidreleasable retaining means is both manually operable and adversecondition responsive.

17. Apparatus of the character set forth in claim 12, and furtherincluding exhaust stack means, and means for directing the flow of saidcooled diluted furnace gases from said mixture outlet to said exhauststack means.

movable closure means being operable to open the interior of saidhousing to atmosphere, conduit means surrounding said air pump means andsaid air inlet, and means within said conduit means for controlling thepath of air flow into said housing.

13. Apparatus for use in a furnace emission control system comprising acap housing mountable on a furnace flue and including sidewall means andmovable closure means, the bottom of said housing being open to saidflue to define a gas inlet to said housing, said sidewall means havingopposed air inlet and mixture outlet openings therein, said housingbeing adapted to receive hot, particle laden gases from said furnaceflue through said gas inlet, flow inducing means for drawing saidfurnace gases into said housing through said gas inlet, an air pump forforcing ambient air under positive pressure directly into said housingthrough said air inlet for said air to mix with, cool and dilute saidgases in said housing, said flow inducing means drawing said cooleddiluted gases through said mixture outlet, said movable closure meansbeing operable to open the interior of said housing to atmosphere,conduit means surrounding said air pump and said air inlet, and meanswithin said conduit means for controlling the path of air flow into saidhousing, said means within said conduit means being baffle meansdisposed between said air pumpand air inlet to direct said air into saidhousing in an annular path, a portion of which air flows in coolingrelationship with the underside of said closure means.

14. Apparatus of the character set forth in claim 13, wherein saidbafi'le means is cone-shaped means disposed within said conduit meanswith the smaller diameter end thereof facing toward said air pump, saidconduit means including a conical wall portion surrounding saidcone-shaped baffle means and radially spaced therefrom to define anannular passageway therebetween.

18. Apparatus of the character set forth in claim 17, wherein said meansfor directing flow of said cooled diluted furnace gases includesserially arranged separator means for separating particles from saidcooled diluted gases, said separator means being disposed between saidgas outlet and said exhaust stack means, and said flow inducing meansbeing exhaust fan means between said separator means and said stackmeans.

19. A method of cooling cupola furnace gases in a eupola emission systemincluding a flue having an outlet end, a chamber at the outlet end ofsaid flue, an exhaust stack, duct means including take-off ducting fromsaid chamber, and means to induce furnace gases to flow from said cupolaflue through said chamber and duct means to said exhaust stack, saidmethod comprising forcing ambient air under positive pressure directlyinto said chamber and into co-mingling relationship with said furnacegases in said chamber to cool said furnace gases in said chamber andreduce the temperature of said gases sufficiently to provide temperatureprotection for said chamber and take-off ducting.

20. The method of claim 19, and forcing said ambient air into saidchamber at a constant volume.

21. A method of treating hot particle laden cupola furnace gases in acupola emission system including a flue having an outlet end, a chamberat the outlet end of said flue, an exhaust stack, particle separatormeans between said chamber and exhaust stack and duct means between saidchamber and separator means and including take-off ducting from saidchamber, said method including inducing furnace gas flow through saidflue, chamber, duct means and separator means to said exhaust stack, andforcing ambient air under positive pressure directly into said chamberand into comingling relationship with said furnace gases in said chamberto cool and dilute said gases prior to flow thereof from said chamber tosaid separator means and exhaust stack and to reduce the temperature ofsaid gases in said chamber sufficiently to provide temperatureprotection for said chamber and take-off ducting.

22. The method of claim 21, and maintaining the flow rate of inducedflow at a constant volume, and forcing said ambient air into saidchamber at a constant volume.

2. Apparatus of the character set forth in claim 1, wherein the axes ofsaid air inlet and said gas inlet are substantially perpendicular to oneanother.
 3. Apparatus of the character set forth in claim 2 wherein theaxis of said mixture outlet is substantially parallel to the axis ofsaid air inlet.
 4. Apparatus for use in an emission control system for afurnace having a flue comprising, a housing at the upper end of saidflue, said housing having a gas inlet, an air inlet and a mixtureoutlet, said housing being adapted to receive hot, particle laden gasesfrom said furnace, flow inducing means for drawing said furnace gasesinto said housing through said gas inlet, and air pump means for forcingambient air under positive pressure directly into said housing throughsaid air inlet for said air to mix with, cool and dilute said gases insaid housing, said flow inducing means drawing said cooled diluted gasesthrough said mixture outlet, conduit means surrounding said air pumpmeans and air inlet, and means within said conduit means for controllingthe path of air flow into said housing.
 5. Apparatus of the characterset forth in claim 4, wherein said means within said conduit means isbaffle means disposed between said air pump means and air inlet. 6.Apparatus for use in a furnace emission control system comprising, ahousing having a gas inlet, an air inlet and a mixture outlet, saidhousing being adapted to receive hot, particle laden gases from saidfurnace, flow inducing means for drawing said furnace gases into saidhousing through said gas inlet, an air pump for forcing ambient airunder positive pressure directly into said housing through said airinlet for said air to mix with, cool and dilute said gases in saidhousing, said flow inducing means drawing said cooled diluted gasesthrough said mixture outlet, conduit means surrounding said air pump andair inlet, and baffle means within said conduit means between said airpump and air inlet, said baffle means being cone-shaped and disposed insaid conduit means with the smaller diameter end thereof facing towardsaid air pump, said conduit means including a conical wall portionsurrounding said cone-shaped baffle means and radially spaced therefromto define an annular passageway for directing said air into said housingin an annular path.
 7. Apparatus of the character set forth in claim 6,wherein said cone-shaped baffle means is axially adjustable relative tosaid conduit means to selectively increase or decrease the radial spacebetween the baffle means and conical wall portion of said conduit means,thus to vary the size of said annular passageway and vary the velocityof air flow into said housing.
 8. Apparatus of the character set forthin claim 1, and further including exhaust stack means, means fordirecting the flow of said cooled diluted furnace gases from saidmixture outlet to said exhaust stack means.
 9. Apparatus of thecharacter set forth in claim 8, wherein said means for directing flow ofsaid cooled diluted furnace gases includes serially arranged separatormeans for separating particles from said cooled diluted gases, saidseparator means being disposed between said gas outlet and said exhauststack means, and said flow inducing means being exhaust fan meansbetween said separator means and said stack means.
 10. Apparatus for usein a furnace emission control system comprising a cap housing mountableon top of a furnace flue and including side wall means and movableclosure means, the bottom of said housing being open to said flue todefine a gas inlet to said housing, said side wall means having opposedair inlet and mixture outlet openings therein, said housing beingadapted to receive hot, particle laden gases from said furnace fluethrough said gas inlet, flow inducing means for drawing said furnacegases into said housing through said gas inlet, conduit meanssurrounding said air inlet, and air pump means in said conduit means andspaced from said air inlet for forcing ambient air under positivepressure directly into said housing through said air inlet for said airto mix with, cool and dilute said gases in said housing, said flowinducing means drawing said cooled diluted gases through said mixtureoutlet, and said movable closure means being operable to open theinterior of said housing to atmosphere.
 11. Apparatus of the characterset forth in claim 10, wherein said means for forcing ambient air underpressure through said air inlet is an air pump.
 12. Apparatus for use ina furnace emission control system comprising a cap housing mountable ona furnace flue and including side wall means and movable closure means,the bottom of said housing being open to said flue to define a gas inletto said housing, said sidewall means having opposed air inlet andmixture outlet openings therein, said housing being adapted to receivehot, particle laden gases from said furnace flue through said gas inlet,flow inducing means for drawing said furnace gases into said housingthrough said gas inlet, an air pump for forcing ambient air underpositive pressure directly into said housing through said air inlet forsaid air to mix with, cool and dilute said gases in said housing, saidflow inducing means drawing said cooled diluted gases through saidmixture outlet, said movable closure means being operable to open theinterior of said housing to atmosphere, conduit means surrounding saidair pump means and said air inlet, and means within said conduit meansfor controlling the path of air flow into said housing.
 13. Apparatusfor use in a furnace emission control system comprising a cap housingmountable on a furnace flue and including sidewall means and movableclosure means, the bottom of said housing being open to said flue todefine a gas inlet to said housing, said sidewall means having opposedair inlet and mixture outlet openings therein, said housing beingadapted to receive hot, particle laden gases from said furnace fluethrough said gas inlet, flow inducing means for drawing said furnacegases into said housing through said gas inlet, an air pump for forcingambient air under positive pressure directly into said housing throughsaid air inlet for said air to mix with, cool and dilute said gases insaid housing, said flow inducing means drawing said cooled diluted gasesthrough said mixture ouTlet, said movable closure means being operableto open the interior of said housing to atmosphere, conduit meanssurrounding said air pump and said air inlet, and means within saidconduit means for controlling the path of air flow into said housing,said means within said conduit means being baffle means disposed betweensaid air pump and air inlet to direct said air into said housing in anannular path, a portion of which air flows in cooling relationship withthe underside of said closure means.
 14. Apparatus of the character setforth in claim 13, wherein said baffle means is cone-shaped meansdisposed within said conduit means with the smaller diameter end thereoffacing toward said air pump, said conduit means including a conical wallportion surrounding said cone-shaped baffle means and radially spacedtherefrom to define an annular passageway therebetween.
 15. Apparatus ofthe character set forth in claim 10, wherein said closure means is apair of doors biased toward an open disposition relative to saidhousing, and means releasably retaining said doors in a closeddisposition against said bias.
 16. Apparatus of the character set forthin claim 15, wherein said releasable retaining means is both manuallyoperable and adverse condition responsive.
 17. Apparatus of thecharacter set forth in claim 12, and further including exhaust stackmeans, and means for directing the flow of said cooled diluted furnacegases from said mixture outlet to said exhaust stack means. 18.Apparatus of the character set forth in claim 17, wherein said means fordirecting flow of said cooled diluted furnace gases includes seriallyarranged separator means for separating particles from said cooleddiluted gases, said separator means being disposed between said gasoutlet and said exhaust stack means, and said flow inducing means beingexhaust fan means between said separator means and said stack means. 19.A method of cooling cupola furnace gases in a cupola emission systemincluding a flue having an outlet end, a chamber at the outlet end ofsaid flue, an exhaust stack, duct means including take-off ducting fromsaid chamber, and means to induce furnace gases to flow from said cupolaflue through said chamber and duct means to said exhaust stack, saidmethod comprising forcing ambient air under positive pressure directlyinto said chamber and into co-mingling relationship with said furnacegases in said chamber to cool said furnace gases in said chamber andreduce the temperature of said gases sufficiently to provide temperatureprotection for said chamber and take-off ducting.
 20. The method ofclaim 19, and forcing said ambient air into said chamber at a constantvolume.
 21. A method of treating hot particle laden cupola furnace gasesin a cupola emission system including a flue having an outlet end, achamber at the outlet end of said flue, an exhaust stack, particleseparator means between said chamber and exhaust stack and duct meansbetween said chamber and separator means and including take-off ductingfrom said chamber, said method including inducing furnace gas flowthrough said flue, chamber, duct means and separator means to saidexhaust stack, and forcing ambient air under positive pressure directlyinto said chamber and into co-mingling relationship with said furnacegases in said chamber to cool and dilute said gases prior to flowthereof from said chamber to said separator means and exhaust stack andto reduce the temperature of said gases in said chamber sufficiently toprovide temperature protection for said chamber and take-off ducting.22. The method of claim 21, and maintaining the flow rate of inducedflow at a constant volume, and forcing said ambient air into saidchamber at a constant volume.